There is a widespread industrial need to provide controllable temporary storage of packages or similar articles. Where this kind of surge or buffering requirement can be filled by using roller conveyors, it then becomes necessary to stop the flow without damaging any articles or packages. Damage can be avoided if collisions or impacts on each other are avoided when packages are brought to a stop, and if package line pressure is avoided after a closed-gap queue of stopped packages is formed-up and waiting. On the other hand, it is desirable to close gaps in order to conserve conveyor space. Thus, an accumulating conveyor system should be impact-free, gap-free, and should permit no line pressure in its handling of articles or packages.
To avoid line pressure build-up in a standing queue of articles on a roller guideway accumulator, driving force on these articles is removed at the point each added article is stopped. This is done by disengaging or declutching rollers from their driving medium. When these rollers are declutched, they are put in a coast (or free-wheeling) mode. Such a coast mode can be effected for a section of rollers upstream of the last package in a queue by placing a sensor a given distance downstream of the rollers being controlled. When each drive roller is individually controlled by its own downstream sensor, a fairly constant length section of coast-mode rollers will be provided at the upstream end of the queue, and this section will automatically move upstream. This downstream sensor arrangement, through its coast-mode section, provides the benefit of eliminating or reducing any impact of each new package adding to the end of the queue. With consistent size and weight packages, coasting distance would be fairly consistent, so that a downstream-sensor kind of accumulator theoretically could be designed or adjusted to practically eliminate both impact and line pressure.
Where it is desired to handle material such as break-bulk freight, package sizes and weights are variable and package surfaces can be expected to have variable friction characteristics on any given set of rollers. These factors contribute to differing coasting distances among different articles. Consequently, some impacts and some gaps, both variable may occur between these packages even in the case of an individual-control, downstream-sensor roller accumulator.
In the zone-control accumulators, where a number of drive-rollers are operated by a single downstream sensor to comprise a zone, another factor of variability is introduced because the sensor can be operated by a large or small package and the package can be mostly downstream or mostly upstream of the sensor. Here the available coast-mode length of conveyor is variable instead of fairly constant. Thus small packages in relatively large zones can be expected to yield gaps in some proportion to the disparity between the size of the package and the size of the zone.
Some prior types of conveyor systems utilize belt drives and pressure rollers for clutching and disengaging the drive rollers. This method requires adjustment for setting the pressure rollers and this adjustment may be a compromise between clutching and disengaging where the latter might be accompanied by residual driving force which produces line pressure build-up.
Some types of these systems use a pressure-air method of actuating in which the inflation of a bladder moves a frame supporting a set of rollers. In one type the pressure rollers are moved. In another type the load rollers are moved.
In these pressure-air actuation methods, the systems use air valves in conjunction with sensor rollers to detect packages. Such valves may prove to be unreliable. In addition, in one system the sensor roller is pivoted at one end of its shaft, while the other end is supported by a spring-loaded member of the valve, so that the roller is canted when no package is on it. If lightweight packages are not directed to pass down the valve side of the conveyor, force on the valve may be negligible, and sensing action may be unreliable according to our experience. In addition, this sensing action may be hampered by binding of the roller shaft in its vertical guide slot.
Another problem with respect to prior art accumulating systems is that it has been necessary to provide continual drive to the rollers in the area where the packages or articles are stopped. As a result, scuffing or wear on the packages may occur.
Accordingly, among the objects of the invention are to provide a roller conveyor system wherein a plurality of zones or areas are automatically declutched upsteam from a stopped article; wherein adjustment for package weight is not required; wherein differing transport speeds are provided in separate zones; and which incorporates a brake type package stop device.